In a case where machining processing is performed over all the surfaces of a workpiece, a clamp device as described above (so called hole clamp device) is employed, since it is not possible to employ a clamp device of the type that presses from above with a pressing implement upon an end portion of the workpiece. With such a clamp device, a seating surface is formed on a body member, on which the workpiece to be the object of clamping is seated. When the workpiece is to be loaded, the workpiece is mounted on this seating surface and is supported thereupon, and a grip member and a clamp rod having a tapered shaft portion inserted into the grip member are inserted into a hole in the workpiece. And next, after increasing the diameter of a grip claw and engaging it against the inner circumferential surface of the hole with the tapered shaft portion by pulling the clamp rod towards the seating surface, the workpiece is fixed against the seating surface by further pulling this grip member towards the seating surface.
Clamp devices like the one described above are disclosed in Patent Documents #1 and #2.
In particular, with the clamp device described in Patent Document #1, in order to cope with variations in the position of the hole in the workpiece, the grip member and the clamping rod having a tapered shaft portion, are adapted to be movable in directions orthogonal to the axis, thereby it is possible to perform reliable clamping, even if the position of the hole in the workpiece is deviated more or less from its proper original position.
Now, generally, often a seating sensor is provided to the seating surface of a clamp device, in order, when fixing a workpiece with the clamp device, to detect whether or not the workpiece has been fixed in the state of being correctly seated to the seating surface. This seating sensor comprises a pressurized air ejection hole that opens to the seating surface, an air supply passage that supplies pressurized air to this pressurized air ejection hole, a pressure switch that detects whether the air pressure within this air supply passage has risen to at least a predetermined pressure, and so on.
Patent Document #1: Japanese Pat. No. 3,550,010 Publication
Patent Document #2: German Pat. No. 4,020,981 Publication
If a seating surface that receives and stops the workpiece and a seating sensor are provided to such a clamp device, then the pressurized air ejection hole of the seating sensor is closed by the wall surface of the workpiece when the workpiece is loaded and seated upon the seating surface. Accordingly, irrespective of whether or not the clamp operation to fix the workpiece is completed, the seating sensor undesirably detects that the workpiece is seated, so that there has been the problem of mistaken determination that the operation of clamping the workpiece has been completed.
Furthermore, with the clamp device of Patent Document #1, in order to make it possible to perform clamping even if the position of the hole in the workpiece is deviated more or less from its proper position, the grip member and the clamp rod having the taper shaft portion are made to be movable in directions orthogonal to their axis. However, no mechanism is provided for returning the grip member and the clamp rod to their original positions (i.e. their center positions) when clamping operation is performed in a state where the grip member and the clamp rod are shifted in a direction orthogonal to the axis, and thereafter the device returns to the unclamped state. Accordingly, it is necessary to perform the troublesome task of manually returning the grip member and the clamp rod to their original positions, and, if this task of returning is neglected, it becomes difficult to insert the grip member and the clamp rod into a hole in a workpiece, and the working efficiency for fixing workpieces decreases.
Apart from this, as described above, when a workpiece is to be clamped with a hole clamp device, in correspondence to the fact that, during clamping, the grip member and the clamp rod are inserted into the hole in the workpiece and the diameter of a grip claw of the grip member is increased, during unclamping, the diameter of the grip claw of the grip member is reduced by the biasing force of an O-ring or the like. However there is the problem that, if the grip claw should bite into the inner surface of the hole in the workpiece, it is not possible reliable to reduce the diameter of the grip claw only with the biasing force due to the O-ring.
An object of the present invention is to provide a clamp device which, directly after loading a workpiece, support this workpiece upon a workpiece mounting surface that shifts integrally with a grip member during clamping operation, and seat the workpiece on a seating surface in a clamped state.
The clamp device according to the present invention comprises an annular grip member capable of expanding and shrinking in a radial direction and moreover of being inserted into a hole in a workpiece and of gripping an inner circumferential surface of the hole, a clamp rod having a tapered shaft portion fitted into and engaged with the grip member, and a fluid pressure cylinder for driving the grip member and the clamp rod forwards and backwards in an axial direction, and is characterized by comprising: a main body member to which the grip member, the clamp rod, and the fluid pressure cylinder are attached; a seating surface formed on the main body member for seating the workpiece; a seating sensor including a pressurized air ejection hole that opens to the seating surface; and a workpiece mounting surface that, when the grip member is at an advanced position in which the grip member is shifted towards the workpiece, can receive and stop the workpiece at a position that is more advanced than the seating surface; and that, during clamp operation in which the grip member and the clamp rod are shifted towards retraction, shifts integrally with the grip member in a direction that is parallel to an axis of the clamp rod.
With this clamp device, when in the unclamped state the workpiece that is to be the object of clamping is loaded, this workpiece is supported on the workpiece mounting surface that is in a position that is more advanced than the seating surface. And when, from this state, the grip member and the clamp rod are driven by the fluid pressure cylinder in the retraction direction to seat and clamp the workpiece, the workpiece mounting surface is shifted towards retraction integrally with the grip member, the state in which the workpiece is seated upon the seating surface is established, and the state of this workpiece fixation is detected by the seating sensor.
According to the present invention, since this clamp device that includes the grip member, the clamp rod, and the fluid pressure cylinder is provided with the main body member, the seating surface formed on the main body member, and the seating sensor, and since the workpiece mounting surface is provided that, when the grip member is in an advanced position that is shifted towards the workpiece, is capable of receiving and stopping the workpiece in a position that is more advanced than the seating surface, accordingly, after the workpiece that is to be the object of clamping has been loaded and before it is clamped, it is possible to support this workpiece on the workpiece mounting surface.
Accordingly, it is possible reliably to prevent the seating sensor operating before clamping. Moreover, the workpiece is seated against the seating surface when the workpiece has been clamped and fixed, and has been fixed in a properly clamped state, it is possible reliably to detect with the seating sensor that the workpiece is fixed in a state in which it is properly seated against the seating surface.
In addition to the structure of the present invention as described above, it would also be acceptable to arrange to employ various further structures, as follows.
(1) The workpiece mounting surface may be formed on the grip member. Since, according to this structure, the workpiece mounting surface is formed on the grip member, accordingly it is possible, during clamping operation, to shift it integrally with the grip member in a direction parallel to the axis thereof.
(2) The workpiece mounting surface may be formed on one or a plurality of workpiece mounting surface forming members that are arranged around the external circumference of the grip member. According to this structure, it is possible to simplify the structure of the grip member by forming one or a plurality of workpiece mounting surface forming members arranged around the outside of the external circumference of the grip member.
(3) The grip member and the clamp rod may be disposed to be movable in directions orthogonal to the axis. According to this structure, even if the position of the hole deviates slightly due to an error while manufacturing the workpiece, still it is possible to perform clamping, via a shift of the grip member and the clamp rod in a direction orthogonal to the axis.
(4) There may be further included an elastic biasing means that elastically biases the grip member and the clamp rod so that the common axis of the grip member and the clamp rod coincides with the axis of the fluid pressure cylinder. According to this structure, when the clamp member is in the unclamped state, the common axis of the grip member and the clamp rod is elastically biased by the elastic biasing means so as to coincide with the axis of the fluid pressure cylinder, and the grip member and the clamp rod automatically return to their original positions in which these two axes agree with one another. Due to this, there is no requirement to perform the troublesome task of returning the grip member and the clamp rod back to their original positions by manual operation.
(5) The fluid pressure cylinder may include: a cylinder bore; a piston member that is installed in this cylinder bore and is linked to the clamp rod; a tubular piston rod that is formed on the piston member; a clamping fluid chamber that is defined within the cylinder bore on a side of the tubular piston rod, and an unclamping fluid chamber that is defined within the cylinder bore on an opposite side to the clamping fluid chamber relative to a piston portion of the piston member; and an annular pressure receiving member that is fitted on the exterior of the tubular piston rod and is movable in a direction parallel to the axis of the clamp rod while being capable of receiving the fluid pressure in the clamping fluid chamber, and that receives and stops a base end surface of the grip member. According to this structure, in the state in which the grip member is supported by the annular pressure receiving member, the clamp rod is driven and radially expands the grip member, and thereafter it is possible to drive the grip member and the clamp rod in the direction to seat and clamp the workpiece.
(6) There may be further comprising an elastic biasing means including an elastic ring member that is installed between the tubular piston rod and the clamp rod in a compressed state, in order to make the common axis of the grip member and the clamp rod coincide with the axis of the fluid pressure cylinder. According to this structure, it is possible to implement the elastic biasing means with a simple structure.
(7) The elastic biasing means may include a scraper made from an elastic material, which is slidable on an outer circumferential surface of an annular guard portion of the grip member and elastically biases the grip member and the clamp rod. According to this structure, the scraper also serves as the elastic biasing means, and it is possible to implement the elastic biasing means with a simple structure.
(8) The grip member may include an annular guard portion on which the workpiece mounting surface is formed, a grip claw portion that extends in the advance direction from this annular guard portion, and a base end guard portion that is formed on an opposite side to the grip claw portion relative to the annular guard portion; and the grip member is consisting of a plurality of separated grip members which are divided at a plurality of positions around its circumferential direction. According to this structure, it is easy for the grip member to increase in diameter during clamping, and moreover it is easy for the grip member to reduce in diameter during clamping release.
(9) The annular pressure receiving member may be disposed to be shiftable in a direction parallel to the axis of the clamp rod through a predetermined stroke between a first position in which the workpiece mounting surface is at a position that is advanced more than the seating surface in the advance direction, and a second position in which the workpiece mounting surface is at a position that is retracted behind the seating surface. According to this structure it is possible reliably to seat the workpiece upon the seating surface while the workpiece is clamped and fixed, since, after the workpiece that is to be the object of clamping has been loaded and before it is clamped, this workpiece is reliably supported by the workpiece mounting surface.
(10) The fluid pressure cylinder may be adapted, during clamping, to drive the clamp rod in the retraction direction, and, during clamping release, to drive the clamp rod in the advance direction; with there being further provided a diameter reduction mechanism that, during the clamping release, establishes a diameter reduced state in which the plurality of separated grip members of the grip member are made to approach towards the clamp rod. According to this structure, during clamping release, it is possible reliable to reduce the diameter of the plurality of separated grip members.
(11) And the diameter reduction mechanism may include a tapered surface formed upon the base end portion of the grip member so as to reduce in diameter downward, and a tapered engagement portion that is formed upon the clamp rod so as to be capable of engaging from below with the tapered surface, and that increases in diameter upward. According to this structure, due to the guidance operation of the tapered surface of the grip member and the tapered engagement portion of the clamp rod, a force for diameter reduction acts from the clamp rod upon the base end point of the grip member, so that during clamping release it is easy reliably to reduce the diameter of the plurality of separated grip members.